Abstract Insomnia is a major public health problem, with significant psychological, health, and economic consequences. Studies have demonstrated that face-to-face cognitive-behavioral therapy (CBT) for insomnia is one of the most effective treatments. Despite the therapeutic effectiveness of CBT, treatment availability is significantly limited by a lack of trained clinicians, poor geographical distribution of knowledgeable professionals, and expense. One way to overcome these barriers is to use the Internet to deliver treatment, potentially making this effective intervention more accessible and less costly. In a recent NIH (R34) study, we developed and tested a self-guided, interactive, tailored Internet intervention for adults with insomnia (SHUTi: Sleep Healthy Using The Internet, www.shuti.net). SHUTi incorporates the primary components of CBT for insomnia, including sleep restriction, stimulus control, cognitive restructuring, sleep hygiene, and relapse prevention. In the small, local RCT, participants who received SHUTi significantly improved their sleep, whereas the wait-list control group showed no significant changes. Moreover, these improvements were maintained at 6 month follow-up. The proposed study will expand on the R34 trial by including a broader sample, comparing SHUTi to a Patient Education website, and conducting follow-up assessments for one-year to demonstrate potential maintenance of treatment effects. In this new RCT, we will recruit 300 adults with insomnia, including those with comorbid psychological or medical conditions, as part of a 2 (Patient Education vs. SHUTi) X 4 (Pre, Post, 6 and 12 month follow-up) study design. We hypothesize that adults who receive SHUTi will show greater improvements in sleep, mood related symptoms, perceived health status, and overall quality of life compared to those receiving the Patient Education website. We believe that use of SHUTi will result in greater efficacy compared to the Patient Education website at only a moderate increase in costs, resulting in a greater cost effectiveness ratio. We will also test our model for Internet interventions, and begin to identify user characteristics that may be predictive in determining symptom improvement. Because Internet interventions may ultimately be able to reduce health disparity by increasing access to care for geographically isolated patients, we will collect data regarding the sample's access to insomnia treatment. Finally, it is important to note that this proposal is consistent with the recommendations made by the 2005 NIH State-of-the-Science for Insomnia Conference Statement calling for increased research on insomnia treatment.